Non-corrodent aqueous media



United States Patent NON-CORRODENT AQUEOUS MEDIA Robert S. Montgomery, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application October 22, 1956 Serial No. 617,260

9 Claims. (Cl. 252392) This invention relates to and has for its principal objective the provision of aqueous media that are tolerable to and not corrosive of various metal surfaces, particularly iron and steel surfaces, and which are especially utile for employment as coolants in metal heat-exchanging systems, water-based cutting fluids and the like.

According to the present invention, a non-corrodent aqueous medium is comprised of water containing a minor proportion of an alcamine salt of coal acids dissolved therein. Advantageously, water may be rendered noncorrosive to metals to provide an aqueous medium in accordance with the invention by incorporating therein between about 0.01 and percent by weight of the alcamine salt of coal acids, based on the weight of the non-corrodent medium. For many purposes it may be more advantageous to employ from 0.1 to 2 percent by weight of the alcarnine salt in the medium. It is desirable for the alcamine salt of coal acids that is employed to be at least substantially neutral to ensure the provision of a neutral aqueous medium. In this connection, it is preferred for the attainment of optimum results to provide a sufliciently alkaline form of the salt so that the aqueous medium has a definite basicity.

The alcamine salt of coal acids that is employed may be obtained readily as the product of the reaction of free coal acids with a suitable alkanolamine. Triethanolamine may be utilized with particular advantage for this purpose although, if desired, other alkanolamines may be beneficially employed, especially low molecular weight alkanolamines such as monoand diethanolamine, mixtures of mono-, diand triethanolamine, propanolamine and the like including low molecular weight polyglycol polyamines. As mentioned, it is desirable to employ an alcamine salt of coal acids that is at least substantially neutral. The basic salts that have been indicated as being preferable should have such a degree of basicity that the pH of the resulting medium is at least about 8.5. As is apparent, such basic salts may be obtained readily by utilizing slightly greater than equivalent proportions of the free coal acids or the alkanolamine, respectively.

The coal acids that are employed to prepare the alcamine salts utilized in the present invention may be identical with or similar to those which may be obtained in a known manner by the oxidation with gaseous oxygen of an aqueous alkaline slurry of finely divided carbonaceous material selected from the group consisting of coal and coke that has been obtained by the carbonization of coal at temperatures beneath about 700 C. Coal acids that have been obtained by the nitric acid oxidation of suitable carbonaceous materials are also generally satisfactory.

The free coal acids are a hygroscopic, usually yellowish, essentially water-soluble material. They are believed to be comprised substantially of various aromatic polycarboxylic acids in a mixture having an average molecular weight in the neighborhood of 250. Their average 2,878,191 Patented Mar. 17, 1959 A cylinder of mild steel was placed in contact with several cast iron strips and the entire assembly immersed in an aqueous 0.5 percent by weight solution of the neutral triethanolamine salt of free coal acids which also contained about 10 percent of a polyglycol. After continuous immersion at room temperature for one week the metals were removed from the solution and examined for evidences of corrosion. None were discernable, although the metals were stained.

EXAMPLE B A number of tests were conducted to determine the corrosiveness to freshly wire-brushed specimens of cast iron, mild steel and formula 921 cast aluminum, wired together with copper. The tests were conducted with various aqueous solutions of triethanolamine salts of coal acids that had differing basicities, as represented by their individual pH values of 8.25, 8.5, 8.75, 9.0 and 9.25. Each of the cast iron pieces had dimensions of about x 1 x 3 inches. The mild steel samples were about A; x 1 x 3 inches in size and the aluminum strips about As x /2 x 9i inches. Formula 921 aluminum meets the following specification for composition:

Component: Percent by weight Copper (Cu) 3.5-4.5 Silicon (Si) 0.75-1.75 Iron (Fe) 1.5 max. Zinc (Zn) 1.5 max. Manganese (Mn) 0.75 max. Magnesium (Mg) 1.5 max. Lead (Pb) 0.5 max. Nickel (Ni) 0.5 max. Aluminum (A1) Balance About six inch lengths of No. 12 copper wire were used for assembly of each composite specimen.

Each of the solutions were prepared by reacting about one milliliter of triethanolamine dissolved in potable tap water (provided by the Water Department of the city of Midland, Michigan) with a sufiicient quantity of free coal acids to achieve the desired indicated pH in each solution. The metal samples were then immersed in the solutions and maintained therein for seven days in sealed containers. At the end of this period, the samples were visually examined. The resulting solutions were also spectroscopically analyzed for their contents of iron, aluminum, copper, magnesium and tin. The results are set forth in the following tabulations; In Table l the visual appearances are denoted and in Table II the results of the analysis of the solutions is given. For purposes of comparison, similar solutions having identical basicities were prepared in the same way excepting to employ lauric acid and acetic acid for formation of the dissolved triethanolamine salts. The results of exactly the same tests with the same metal specimens are also included in the following tabulation. It is to be noted that, in certain cases, the products of any corrosion that occurred were soluble and in others they were at least 'to the suggestions of U. S. Patents Nos.

I partially insoluble. This fact may be pertinent to clarify certain discrepancies that might otherwise be indicated between portions of the data in Tables I and II. In addition to. what is set forth in the tables, all of'the metal samples immersed in the triethanolamine-acetic acid salt solutions were observed to have become stained to an extreme degree- The reasons for employing'lauric and acetic acid salts of triethanolamine for comparative purposes were that lauric acid, an aliphatic acid containing more than ten carbon atoms in its molecule, is used extensively in corrosion-inhibitors (as would be pursuant 1,992,689; 2,018,758 and 2,126,173) and the solubility characteristics of acetic acid are about commensurate with those of coal acids.

minor proportions of the same salt andother alcamine salts of free coal acids.

The alcamine salts of coal acids are not. only exceptionally efficacious corrosion inhibitors. for water that are stable for long periods over a wide range and variety Table I.-Visual appearance of metal specimens Castiron Mild steel Aluminum alloy Copper pH of solution Coal Acetic Laurie Coal Acetic Laurie Coal Acetic Laurie Coal Acetic Laurie acid ,aeid acid acid acid acid acid acid acid acid acid acid salts salts salts. salts salts salts salts salts salts salts salts salts 0.11--.. Oorrodedn Corroded O.K. O.K O.K. usted OK do do 0.K. 0.1K-.-" O.K. rln 0..-"--- O.K- O.K----.. O.K. .'.do 0 O T O 1 OK. 0 K dn 0 R O V 0 TC OlK. O.K do O.K. O.K- O.K..- O.K.

1 Denotes H value of 8.0.

Table II.-Metal ions formed in various solutions Percent by weight iron Percent by weight Percent by weight copper Percent by weight Percent by weight tin' aluminum magnesium p1? of so utlon Coal Acetic Laurie Coal Acetic Laurie Coal Acetic Laurie Coal Acetic Laurie Coal Acetic Laurie acid acid acid acid acid acid acid acid acid acid acid acid acid acid acid salts I salts salts salts salts salts salts salts salts I salts salts salts salts salts salts 1 Denotes pH value of 8.0.

EXAMPLE C 3. The composition of claim 1, wherein the salt is A freshly mirror polished mild steel strip having dimensions of about A; x 1 x 2 /2 inches was placed in an aqueous composition that consisted of 175 grams of distilled water, 1.1 grams of triethanolamine and 0.1 gram of coal acids which was contained in a 250 milliliter round-bottomed flask. The solution had a pH of about 8.9. In general conformation with a procedure that has been suggested and employed by the E. F. Houghton Company, the solution, from whose surface a part of the metal strip projected, was refluxed at atmospheric pressure for four weeks using a very wide reflux condenser to permit free access of oxygen into the flask. At the end of this period there was absolutely no corrosion of the submerged portion of the metal. Better yet, it had maintained its mirror-bright finish throughout the test. The projecting portion of the sample was observed to corrode to only a very slight extent. This was not surprising since the salt of triethanolamine and coal acids is not volatile and the projecting portion of the sample was thus contacted with only uninhibited water vapor containing triethanolamine it; the presence of air. An identical metal specimen which was tested in the foregoing manner with plain water was noted to rust badly within a few hours of the commencement of the test with the water becoming completely turbid with rust within only one day's time.

Excellent results similar to the foregoing may be obbasic.

4. The composition of claim 1, wherein the salt has a sufficient alkalinity to provide said medium with a pH of at least about 8.5

5. The composition of claim 1, wherein the salt is the triethanolamine salt of coal acids.

6. Method for rendering water noncorrosive to metals, particularly iron and steel, which comprises dissolving in the water between about 0.01 and 5 percent by weight of a non-acidic alcamine salt of coal acids.

7. The method of claim 6, wherein the salt is sufficiently alkaline to provide a pH of at least about 8.5 in the resulting solution.

8. The method of claim 6, wherein the salt is a triethanolamine salt of coal acids.

9. The method of clai1n7, wherein the salt is a basic triethanolamine salt of coal acids.

References Cited in the file of this patent UNITED STATES PATENTS 2,018,758 Ellis Oct. 29, 1935 2,126,173 Clapsadle Aug. 9, 1938 2,516,640 Montgomery et al. July 25, 1950 2,545,169 Salathiel Mar. 13, 1951 2,739,871 Senkus Mar. 27, 1956 OTHER REFERENCES Orangic Acids by Direct Oxidation of Coal, Chemitained with other aqueous solutions containing varied cal Industries, April 1946, pages 580 and 581. 

1. NON-CORRODENT AQUEOUS COMPOSITION COMPRISING WATER AND DISSOLVED MINOR PROPORTION OF FROM ABOUT 0.01 TO ABOUT 5 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE COMPOSITION, OF A NON-ACIDIC ALCAMINE SALT OF COAL ACIDS. 